Elm Spanworm

Elm Spanworm (Ennomos subsignarius) - Elm spanworm, is a native geometrid moth whose polyphagous larvae feed on many species of hardwood trees, especially hickory, oak, and ash. It is most important as a forest pest in the Appalachian Mountains, from Pennsylvania south, but an urban forest outbreak has also occurred in St. John's, Newfoundland and Labrador. This species overwinters as eggs, which are laid in clusters on the bole and on the underside of branches. Eggs hatch in early spring and young larvae feed on the lower surfaces of leaves, producing "shot-hole" damage. Older larvae consume the whole leaf apart from the major veins. After developing through five instars, larvae pupate in loose silk cocoons formed on the partly eaten foliage and in bark crevices. Outbreaks of this species occur at irregular intervals that defoliate trees over wide areas.

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